The lubrication system utilized in most air compressors, including the Westinghouse "3-CD" series two stage air compressor, has remained virtually unchanged since the 1940's. Ensuring adequate lubrication, however, has been a continuing design problem.
The lubrication system presently utilized in many compressors draws oil or other lubricating fluid from a sump located within the crankcase, in the same manner that water is "drawn" from a farmer's hand well pump. This lubrication system typically comprises a cartridge having inlet and discharge check valves, a hollow pump plunger having one end driven off an eccentric on the crankshaft to provide both an oscillating and reciprocating motion, and a pump body to house the plunger and cartridge. In operation, rotation of the crankshaft causes the plunger to reciprocate in the pump body, thereby drawing lubricating fluid from an underlying sump through the cartridge inlet and discharge check valves and into the plunger's hollow interior. From the interior of the plunger, lubricating fluid is directed through passageways associated with the crankshaft to wear areas by means of positive pressure.
It has been found that the single reciprocating pumping action of present lubrication systems results in undesirable pressure pulses. Moreover, such systems have been found to provide a relatively low output volume and pressure. To overcome these deficiencies, the present invention employs a positive displacement rotary pump capable of delivering a continuous flow of lubricating fluid, thereby providing a significantly higher overall system pressure and volume.
Conventional lubricating systems also provide only minimal filtration of the lubricating fluid through use of a coarse screen, typically placed in front of the pump inlet. The present invention recognizes the need for increased filtration of the lubricating fluid to minimize wear of the pump and compressor and thus calls for a replaceable filter module which is mountably attached to a removable inspection plate on the exterior of the compressor. This combination of an externally mounted filter module and removable inspection plate provides for the removal of particulate matter which can greatly reduce the useful life of bearings and other moving components, while at the same time providing a viewing port for inspection and maintenance.